In recent years, the number of lung cancer patients continues to increase all around the world, and approximately one million people are currently dying of lung cancer worldwide each year. Also in Japan, lung cancer deaths are increasing, and estimated to reach 123,000 in 2015. Lung cancer is more prevalent among males, and the male-female ratio is three to one. Lung cancer surpassed stomach cancer in 1993 to be the leading cause of cancer death among males. Furthermore, with an increasing number of female smokers, the number of female patients is expected to rise. Lung cancer has been the leading cause of cancer death since 2000, and with the aging society, the number of patients is expected to increase further in the future. Smoking is considered to be the greatest cause of lung cancer development, and other causes are inhalation of asbestos, air pollution, and such. Early detection and prompt treatment are important for lung cancer therapy. However, it has been recently pointed out that simple chest X-ray and sputum test performed during a medical examination are not effective for early detection of lung cancer, and they do not lead to reduction of cancer deaths. Since the number of lung cancer deaths is expected to continue rising in the future, it is an urgent task to develop new therapeutic strategies.
In Japan, the number of biliary tract cancer deaths is on the rise, and in 2005, 16,586 people died of biliary tract cancer. In most biliary tract cancer cases, no subjective symptoms are found in the early stages. Compared to cancers that form in the digestive tract lumen, such as stomach cancer and colon cancer, biliary tract cancer is difficult to find and diagnose at the early stages. Therefore, in many cases, the cancer has already progressed and is unresectable when it is found. In addition to surgical therapy, radiation therapy and chemotherapy are performed for biliary tract cancer, but they are not therapeutically effective, and it is necessary to establish new therapeutic method.
On the other hand, recent development in molecular biology and tumor immunology has elucidated that cytotoxic (killer) T cells and helper T cells recognize peptides generated by degradation of proteins that are specifically and highly expressed in cancer cells, and which are presented on the surface of cancer cells or antigen presenting cells via HLA molecules and cause immunoreaction to destroy cancer cells. Furthermore, many tumor antigen proteins and peptides derived therefrom, which stimulate such immunoreaction to attack cancer, have been identified, and antigen-specific tumor immunotherapy is being clinically applied.
The HLA class I molecule is expressed on the surface of all nucleated cells of the body. It binds to a peptide generated by intracellular degradation of proteins produced in the cytoplasm or nucleus, and expresses the peptide on the cell surface. On the surface of a normal cell, peptides derived from normal autologous proteins bind to HLA class I molecules, and are not recognized and destroyed by T cells of the immune system. On the other hand, in the process of becoming a cancer, cancer cells sometimes express a large quantity of proteins that are hardly or slightly expressed in normal cells. When HLA class I molecules bind to peptides generated by intracellular degradation of proteins specifically and highly expressed in cancer cells, and then express the peptides on the surface of cancer cells, cytotoxic (killer) T cells recognize and destroy only the cancer cells. By administering such cancer-specific antigens or peptides to an individual, cancer cells can be destroyed and cancer growth can be suppressed without harming normal cells. This is called cancer immunotherapy using cancer-specific antigens. HLA class II molecules are mainly expressed on the surface of antigen-presenting cells. The molecules bind to peptides derived from cancer-specific antigens, which are generated by intracellular degradation of cancer-specific antigens incorporated into antigen-presenting cells from outside of the cells, and then express the peptides on the surface of the cells. Helper T cells that recognize them are activated, and induce or enhance immunoreaction against tumors by producing various cytokines that activate other immunocompetent cells.
Accordingly, if an immunotherapy that targets antigens specifically and highly expressed in cancers is developed, such a therapy can effectively eliminate cancers alone without causing any harmful event on normal autologous organs. It is also expected that the therapy can be used for any terminal cancer patients to whom other treatments cannot be applied. In addition, by administering a cancer-specific antigen and peptide as a vaccine in advance to individuals with a high risk of developing cancers, cancer development can be prevented.
Although there are various therapeutic methods for lung cancer, the lung cancer results in poor prognosis compared to other cancers, and it is one of the intractable cancer. The reason is, for example, rapid progression, and in many cases, the cancer has advanced by the time it is found. Furthermore, since the surgery is highly invasive, patients who is applicable with the surgery are limited, and complete cure by radiation therapy or chemotherapy is difficult. If an immunotherapy targeting antigens that are highly and specifically expressed in lung cancer is developed, cancer alone can be effectively eliminated by such therapeutic method without any damage on the normal autologous organs. Furthermore, such therapeutic method is expected to be applicable to any terminal cancer patient, and patients who are not applicable with other treatments due to extremely poor lung function. In addition, since the risk for lung cancer development is high among smokers, immunotherapy may be applicable for prevention of lung cancer in a high-risk group of lung cancer.
By genome-wide gene expression analysis using cDNA microarrays, the present inventors examined the expression profile of 27,648 human genes in 37 clinical cases of non-small-cell lung cancer and in embryonic organs, and various normal adult organs. As a result, the inventors found that CDCA1 (cell division cycle associated 1, also known as human homologues of Nuf2 (hNuf2)) (GenBank Accession No. NM—145697) was highly expressed in many lung cancer cases, while it was hardly expressed in the embryonic liver or normal adult organs except in the testis isolated from the immune system. Furthermore, CDCA1 was highly expressed in all cases of cholangiocellular carcinoma, bladder cancer, and renal cell carcinoma. High CDCA1 expression was also observed in the cancer tissues of 40% or more cases of prostate cancer, chronic myelogenous leukemia, malignant lymphoma, cervical cancer, osteosarcoma, breast cancer, soft tissue sarcoma, and colon cancer. This fact suggests that CDCA1 could serve as a cancer-specific antigen in many carcinomas.
HLA-A2 is frequently observed in human populations regardless of the race, and is possessed by about 30% of the Japanese. Therefore, if one can identify a cancer antigen peptide that is presented to cytotoxic (killer) T cells by HLA-A2, it can be widely applied to not only the Japanese but also Caucasians and such. Accordingly, it is an important task to identify cancer antigen peptides that are presented to killer T cells by HLA-A2. It would be highly beneficial if such cancer antigen peptides are applicable to immunotherapy for lung cancer, which have high morbidity and mortality all over the world.
Prior art documents related to the present invention are shown below.    [Non-patent document 1] DeLuca J. G., Moree, B., Hickey, J. M., Kilmartin, J. V., and Salmon, E. D., hNuf2 inhibition blocks stable kinetochore-microtubule attachment and induces mitotic cell death in HeLa cells J. Cell Biol. 159: 549-555, 2002.    [Non-patent document 2] DeLuca, J. G., Dong, Y., Hergert, P, Strauss, J., Hickey, J. M., Salmon, E. D., McEwen, B. F., Hec1 and Nuf2 Are Core Components of the Kinetochore Outer Plate Essential for Organizing Microtubule Attachment Sites., Mol. Biol. Cell 16: 519-531, 2005.    [Non-patent document 3] Hayama, S., Daigo, Y., Kato, T., Ishikawa, N., Yamabuki, T., Miyamoto, M., Ito, T., Tsuchiya, E., Kondo, S., and Nakamura, Y, Activation of CDCA1-KNTC2, Members of Centromere Protein Complex, Involved in Pulmonary Carcinogenesis., Cancer Res. 66: 10339-10348, 2006.    [Non-patent document 4] Liu, S. T., Rattner, J. B., Jablonski, S. A., and Yen, T. J., Mapping the assembly pathways that specify formation of the trilaminar kinetochore plates in human cells., J. Cell Biol. 175: 41-53, 2006.    [Non-patent document 5] DeLuca, J. G., Howell, B. J., Canman, J. C., Hickey, J. M., Fang, G., and Salmon, E. D., et al. Nuf2 and Hec1 Are Required for Retention of the Checkpoint Proteins Mad1 and Mad2 to Kinetochores., Current Biology 13: 2103-2109, 2003.    [Non-patent document 6] Liu, D., Ding, D., Du, J., Cai, Xin., Huang, Y., Ward, T., Shaw, A., Yang, Y, Hu, R., Jin, C., and Yao, X., Human NUF2 Interacts with Centromere-associated Protein E and Is Essential for a Stable Spindle Microtubule-Kinetochore Attachment. J. Biol. Chem. 282: 21415-21424, 2007.